Rhabditid Nematode-Associated Ophthalmitis and Meningoencephalomyelitis in Captive Asian Horned Frogs (\u3ci\u3eMegophrys montana\u3c/i\u3e) [Case reports]

Between 2006 and 2008, 4 captive Asian horned frogs (Megophrys montana) were diagnosed with ocular and neurologic disease associated with rhabditid nematodiasis. Mortality, either spontaneous or by humane euthanasia, was high (3/4, 75%). Gross and histologic findings included varying degrees of ulcerative keratitis, histiocytic uveitis and retinitis, meningoencephalomyelitis, and epidermal chromatophore (iridophore) hyperplasia with intralesional nematodes. Entry into the host was presumed to be by direct invasion of the skin and the cornea with migration through the optic nerve to the brain and spinal cord. One frog was diagnosed with rhabditid nematodiasis antemortem, and clinical signs and lesions in the frog did not progress after unilateral enucleation and anthelminthic treatment were completed. Gross and tissue morphology of the nematodes were consistent with the order Rhabditida. DNA was extracted separately from 2 individual nematodes that were isolated from frozen and ethanol-preserved eye and brain tissue. These DNA templates were used for polymerase chain reaction amplification and sequencing of nuclear 28S large subunit (LSD) and internal transcribed spacer (ITS) ribosomal DNA regions. Comparison of the LSD and ITS sequences to those deposited in GenBank revealed an exact match for Caenorhabditis elegans

A Reservoir Species for the Emerging Amphibian Pathogen Batrachochytrium dendrobatidis Thrives in a Landscape Decimated by Disease

Chytridiomycosis, a disease caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is driving amphibian declines and extinctions in protected areas globally. The introduction of invasive reservoir species has been implicated in the spread of Bd but does not explain the appearance of the pathogen in remote protected areas. In the high elevation (>1500 m) Sierra Nevada of California, the native Pacific chorus frog, Pseudacris regilla, appears unaffected by chytridiomycosis while sympatric species experience catastrophic declines. We investigated whether P. regilla is a reservoir of Bd by comparing habitat occupancy before and after a major Bd outbreak and measuring infection in P. regilla in the field, monitoring susceptibility of P. regilla to Bd in the laboratory, examining tissues with histology to determine patterns of infection, and using an innovative soak technique to determine individual output of Bd zoospores in water. Pseudacris regilla persists at 100% of sites where a sympatric species has been extirpated from 72% in synchrony with a wave of Bd. In the laboratory, P. regilla carried loads of Bd as much as an order of magnitude higher than loads found lethal to sympatric species. Histology shows heavy Bd infection in patchy areas next to normal skin, a possible mechanism for tolerance. The soak technique was 77.8% effective at detecting Bd in water and showed an average output of 68 zoospores per minute per individual. The results of this study suggest P. regilla should act as a Bd reservoir and provide evidence of a tolerance mechanism in a reservoir species

Evidence for disease-related amphibian decline in Colorado

The recent discovery of a pathogenic fungus (Batrachochytrium dendrobatidis) associated with declines of frogs in the American and Australian tropics, suggests that at least the proximate cause, may be known for many previously unexplained amphibian declines. We have monitored boreal toads in Colorado since 1991 at four sites using capture–recapture of adults and counts of egg masses to examine the dynamics of this metapopulation. Numbers of male toads declined in 1996 and 1999 with annual survival rate averaging 78% from 1991 to 1994, 45% in 1995 and 3% between 1998 and 1999. Numbers of egg masses also declined. An etiological diagnosis of chytridiomycosis consistent with infections by the genus Batrachochytrium was made in six wild adult toads. Characteristic histomorphological features (i.e. intracellular location, shape of thalli, presence of discharge tubes and rhizoids) of chytrid organisms, and host tissue response (acanthosis and hyperkeratosis) were observed in individual toads. These characteristics were indistinguishable from previously reported mortality events associated with chytrid fungus. We also observed epizootiological features consistent with mortality events associated with chytrid fungus: an increase in the ratio of female:male toads captured, an apparent spread of mortalities within the metapopulation and mortalities restricted to post metamorphic animals. Eleven years of population data suggest that this metapopulation of toads is in danger of extinction, pathological and epizootiological evidence indicates that B. dendrobatidis has played a proximate role in this process

Leaping Forward In Amphibian Health And Nutrition

The Epidemiology Working Group, a subgroup of the participants of the Disney\u27s Animal Kingdom Workshop on Ex situ Amphibian Medicine and Nutrition, identified a critical need to design and implement approaches that will facilitate the assessment and evaluation of factors impacting amphibian health. In this manuscript, we describe and summarize the outcomes of this workshop with regards (a) the identified gaps in knowledge, (b) identified priorities for closing these gaps, and (c) compile a list of actions to address these priorities. Four general areas of improvement were identified in relation to how measurements are currently being taken to evaluate ex situ amphibian health: nutrition, infectious diseases, husbandry, and integrated biology including genetics and endocrinology. The proposed actions that will be taken in order to address the identified gaps include: (1) identify and quantify major health issues affecting ex situ amphibian populations, (2) identify and coordinate laboratories to conduct analyses using standardized and validated protocols to measure nutritional, infectious diseases, genetic, and hormonal parameters, (3) determine in situ baseline distribution of parameters related to amphibian health, and (4) establish an inter-disciplinary research approach to target specific hypotheses related to amphibian health such as the effects of population genetics (e.g., relatedness, inbreeding) on disease susceptibility, or how environmental parameters are related to chronic stress and hormone production. We think is important to address current gaps in knowledge regarding amphibian health in order to increase the probability to succeed in addressing the issues faced by in situ and ex situ amphibians populations. We are confident that the recommendations provided in this manuscript will facilitate to address these challenges and could have a positive impact in both the health of in situ and ex situ amphibian populations, worldwide

Habitat occupancy before and after disease spread.

<p>Range of <i>P. regilla</i> and <i>R. muscosa</i> in 60 Lake Basin (a) before and (b) after the spread of <i>Bd</i> through the basin.</p

Histological view of skin from lethally infected individual.

<p>Photomicrograph of a histologic section of the ventral abdominal skin from <i>P. regilla</i> #1 (the only individual that died in captive experiment). There is diffuse severe hyperkeratosis with high numbers of <i>Bd</i> thalli (arrows). This lesion is consistent with lethal chytridiomycosis. E = epidermis.</p

Correlation of <i>Bd</i> detection by swab versus soak.

<p>Soak and swab detection levels were correlated (r² = 0.6543, P = 0.0002605, n = 10). Soaks were 77.8% effective at detecting zoospores detected by swab.</p